DESCRIPTION (Applicant's abstract): Impairment of coronary vasofunction is believed to be one of the earliest manifestations of coronary heart disease (CHD). The impact of risk factors such as elevated cholesterol levels, diabetes, hypertension, and smoking on the coronary microcirculation remains largely unknown. Our major objective is to investigate in a cross-sectional study whether an impairment of the myocardial perfusion reserve provides a marker of CHD by comparing it to other novel measures of subclinical vascular disease, and by testing its association with risk factors for CHD. The proposed study is ancillary to the Multi-Ethnic Study of Atherosclerosis ("MESA"), which is an NHLBI funded, prospective observational study of the characteristics of subclinical cardiovascular disease, i.e. disease detected non-invasively before it has produced signs and symptoms. In MESA new measures of subclinical disease such as coronary artery calcium and impaired brachial artery reactivity are to be examined to investigate their relationships to well-established risk factors and clinical events. We believe that myocardial perfusion reserve (MPR)is a useful measure of coronary vasofunction that should be included in an evaluation of new measures of subclinical disease. An impaired MPR appears to be a specific early indicator of the functional impairment of the microcirculation in patients with risk factors for coronary artery disease. We propose to use magnetic resonance imaging (MRI) as an advanced, quantitative imaging modality to determine in short (20 minute) exams the myocardial perfusion reserve in a group of 400 MESA participants. We hypothesize that impaired myocardial perfusion reserve indicates the presence of subclinical coronary atherosclerosis and coronary microvascular disease. As CHD remains the leading cause of death in the U.S. there is strong interest in developing such new measures of subclinical disease which would provide an early opportunity for intervention and lifestyle modification to prevent CHD and/or congestive heart failure.